1. Field of the Invention
This invention relates to electronic three-dimensional (3D) displays that do not require stereo-glasses, specifically to real-time autostereoscopic or automultiscopic displays.
2. Description of Prior Art
Previous real-time 3D imaging systems that do not require headgear have not been ideal for consumer applications such as 3D television, 3D video games, 3D advertising, or 3D presentations, Nor have they been ideal for many nonconsumer applications such as 3D computer imaging. Of those systems, real-time autostereoscopes that present only a left-eye view and a right-eye view are difficult to use because they need to be viewed from specific viewing locations. Prior art autostereoscopes that are capable of tracking a viewer's eyes and directing each image toward the appropriate eye solves the problem, but at the expense and complication of an added head tracking system. Yet even a head tracking autostereoscope cannot easily accommodate multiple simultaneous viewers, since multiple viewers move their heads independently of each other. The best solution is an automultiscopic display that presents many views. ("Automultiscopic" is a more general term then "autostereoscopic" as used herein. Herein, autostereoscopic displays present exactly two views, whereas automultiscopic displays present two or more views.) Automultiscopic displays typically present many views of an image, allowing observers to move freely and see new perspectives by means of horizontal, and sometimes vertical, parallax. Automultiscopes usually provide the viewer with the ability to "look around" objects by intuitively moving his head.
In the present inventor's U.S. Pat. No. 5,111,313, he describes a simple automultiscopic display. That display, however, requires a moving part and is not a flat panel display. Newswanger, in U.S. Pat. No. 4,799,739, reveals a solid state automultiscopic system. However, Newswanger's system requires several two-dimensional (2D) image projectors that must be aligned and serviced, making it bulky, complex, and costly, and thus not ideal for consumer use. Eichenlaub, in U.S. Pat. Nos. 4,367,486, 4,717,949, and 4,829,365, describes a solid state nearly flat panel 3D automultiscopic display that requires two very fast switching light valve arrays. However, no light valve arrays are available that can switch fast enough to support the many views needed (20-40) to provide fluid and imperceptible changes in perspective as the viewer moves his head.
Lenticular screens, as in prior art FIGS. 1 and 2, have long been a popular approach to 3D imaging. In typical lenticular screen systems of the prior art, an array of long, thin cylindrical lenses 30 is placed in front of a 2D imaging surface 31. If the 2D imaging surface 31 is positioned so as to be at the focal distance of the cylindrical lenses 30, as FIG. 1 shows, a 3D image can be presented via horizontal parallax. Different sets of pixels are observable from different viewing angles, and thus the 3D image is autostereoscopic or automultiscopic. FIG. 1 illustrates how two pixels, 32 and 33, are viewable from unique viewing zones. The pixels on 2D imaging surface 31 are spatially multiplexed by lenticular screen 30. A real-time display could be made employing a lenticular sheet and a real-time 2D display such as a Liquid Crystal Display (LCD) panel. However, the LCD pixels would have to be extremely narrow (0.0025 inch or less to provide 20-40 views) in order for the images viewed to have proper picture element size and shape. The off-axis close-up view of the display in FIG. 2 shows the unusually narrow shape of pixels 32, 33, and all the other pixels on 2D imaging surface 31. Not only do these narrow pixels make alignment of the LCD display and the lenticular screen hypercritical, but the optical imperfections (such as astigmatism, spherical aberration, coma, etc.) of the simple cylindrical lenses that make up the lenticular screen become apparent.
The present disclosed invention achieves superior automultiscopic results than the aforementioned lenticular screen system by using HOEs (Holographic Optical Elements), instead of conventional lenticular screens, as discussed below in combination with the included figures.